Compound, a molecular switch employing the compound and a method of electronic switching

ABSTRACT

Classes of molecules are disclosed which can, for example, be used in molecular switches. The classes of molecules include at least three segments—an electronic donor (“D”), a switchable bridge (“B”), and an electronic acceptor (“A”)—chemically connected and linearly arranged (e.g., D-B-A). The electronic donor can be an aromatic ring system with at least one electron donating group covalently attached; an aromatic ring system with an electron withdrawing group covalently attached is usually employed as the electronic acceptor; and the switchable bridge can be a pi system that can be switched on or off using an external electric field.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 10/946,288,filed Sep. 22, 2004, the contents of which are incorporated herein byreference.

BACKGROUND

Molecular scale electronics, including molecular rectifiers, is anactive area of research. A simple electronic device constructed out of asingle organic molecule, such as a rectifier, can consist of a donorπ-system and an acceptor π-system separated by a sigma-bonded methylenebridge. Semiquantitative calculations can be performed on a hemiquinoneto support the concept.

Molecular electrical rectification can also be observed inLangmuir-Blodgett multilayers or monolayers of γ-hexadecylquinoliniumtricyanoquino-dimethanide sandwiched between metallic electrodes.However, the mechanism of rectification is not necessarily thedonor-insulator-acceptor mechanism. Rather, the envisioned insulator(i.e., sigma-bonded methylene bridge) does not sufficiently isolate thedonor pi system from the acceptor pi system.

SUMMARY

A compound is disclosed having a structure:

wherein “EWG” is selected from a group consisting of —C(═O)H, —C(═O)R₃,—C(═O)OR₃, —C(═O)OH, —CN, —N═O, —NO₂, —SO₂OH, —N═N—, CH═NR₃, —CR₃═NR₄,—C═C(CN)₂, —C═C(COR₃)₂, —C═C(CO₂R₃)₂, —C═C(COR₃)CO₂R₄, —SO₂OR₃,—S(═O)—R₃, —SO₂R₃, —BH₂, —BHR₃, —BR₃R₄, —PO₃H₂, —PO₃R₃R₄, wherein R₃ andR₄ are substituents independently selected from linear alkyl, branchedalkyl, cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted. “EDG” is selected from agroup consisting of —O—, —OH, —OR₁, —NH—, —NH₂, —NHR₁, —NR₁R₂, —PR₁R₂,—PHR₁, —S—, —SH, —SR₁, F, Cl, Br, and I, wherein R₁ and R₂ aresubstituents independently selected from linear alkyl, branched alkyl,cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted. X₁ and X₂ areindependently selected from a group consisting of hydrogen, F, Cl, Br,and I, —OH, —SH, —NH₂; and substituted alkyl groups. G₁-G₂ and G₃-G₄ areindependently selected from a group consisting of —CH═CH—, —CH═CR₅—,—CR₅═CR₆—, —CH₂C(═O)—, —CR₅HC(═O)—, —CC—, —N═N—, —N═CH—, —NH—CO—,—N═C(NH₂)—, —N═C(SH)—, —NCS—, —NH—O— and —NHNH—, wherein R₅ and R₆ aresubstituents independently selected from linear alkyl, branched alkyl,cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted. Z is selected from agroup of atomic units consisting of —CH═, —N═, —S—, —O—, and —P═.

A compound is also disclosed having a structure:

wherein “EWG” is selected from a group consisting of —C(═O)H, —C(═O)R₃,—C(═O)OR₃, —C(═O)OH, —CN, —N═O, —NO₂, —N═N—, CH═NR₃, —CR₃═NR₄,—C═C(CN)₂, —C═C(COR₃)₂, —C═C(CO₂R₃)₂, —C═C(COR₃)CO₂R₄, —SO₂OH, —SO₂OR₃,—S(═O)—R₃, —SO₂R₃, —BH₂, —BHR₃, —BR₃R₄, —PO₃H₂, —PO₃R₃R₄, wherein R₃ andR₄ are substituents independently selected from linear alkyl, branchedalkyl, cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted. “EDG” is selected from agroup consisting of —O—, —OH, —OR₁, —NH—, —NH₂, —NHR₁, —NR₁R₂, —PHR₁,—PR₁R₂, —S—, —SH, —SR₁, F, Cl, Br, and I, wherein R₁ and R₂ aresubstituents independently selected from linear alkyl, branched alkyl,cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted. G₁-G₂ is selected from agroup consisting of —CH═CH—, —CH═CR₅—, —CR₅═CR₆—, —CH₂C(═O)—,—CR₅HC(═O)—, *—CC—, —N═N—, —N═CH—, —NH—CO—, —N═C(NH₂)—, —N═C(SH)—,—NCS—, —NH—O— and —NHNH—, wherein R₅ and R₆ are substituentsindependently selected from linear alkyl, branched alkyl, cyclic alkyl,and an aromatic ring system, and wherein the alkyl substituents aresubstituted or unsubstituted.

A molecular diode switch is disclosed which includes a compound of astructure D-B-A, wherein “D” is an electronic donor, “B” is a switchablebridge, and “A” is an electronic acceptor; and two electrodes inoperable contact with the compound.

A disclosed method of electronic switching includes applying an electricfield of a first polarity to a compound, wherein the compound is of astructure D-B-A, and wherein “D” is an electronic donor, “B” is aswitchable bridge, and “A” is an electronic acceptor, to cause a firstconformational change in the compound that allows electron conductancethrough the compound's π-system; and applying an electric field of asecond, opposite polarity to the compound, thereby causing a secondconformational change in the compound that inhibits electron conductancethrough the compound's pi system.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of preferred embodiments can be readin connection with the accompanying drawings in which like numeralsdesignate like elements and in which:

FIG. 1 shows an exemplary subclass of molecules disclosed herein.

FIG. 2 shows a second exemplary subclass of molecules disclosed herein.

FIG. 3 shows an exemplary synthetic scheme for the production of acompound, where X is hydrogen.

FIG. 4 illustrates an exemplary molecular switch using a genericcompound disclosed herein.

FIG. 5 illustrates an exemplary molecular switch that includes amolecule subclass.

FIG. 6 illustrates an exemplary method of switching using a genericcompound disclosed herein.

FIG. 7 illustrates an exemplary method of switching using a moleculeclass.

FIG. 8 illustrates an exemplary method where the compound of themolecular switch includes a switchable bridge.

DETAILED DESCRIPTION

Classes of molecules are disclosed herein that can be employed inmolecular switches. Molecular switches containing the molecule classes,and methods of electronic switching using the molecule classes are alsodisclosed.

Exemplary classes of molecules disclosed herein include a moleculehaving at least three segments—an electronic donor (“D”), a switchablebridge (“B”), and an electronic acceptor (“A”)—chemically connected andlinearly arranged (e.g., to form a compound of the structure D-B-A). Theelectronic donor can be an aromatic ring system with at least oneelectron donating group covalently attached; an aromatic ring systemwith an electron withdrawing group covalently attached can be employedas the electronic acceptor; and, the switchable bridge can be a π-systemthat can be switched on or off using an external electric field.

The bridge can be switched “on” by inducing a change in the molecule'sconformation. Where the π-system of the bridge is out of plane relativeto the pi systems of the electronic donor and acceptor (i.e., anglebetween 10° and 170°, or a range which is lesser or greater, such asbetween 30° to 150°), the molecule has a large HOMO/LUMO band gap; thereis a tunneling distance across the bridge which can be significant(e.g., >1 nm). These features make the bridge effectively operate as aninsulator.

When an external electronic field with an appropriate orientation isapplied, however, the molecule will tend to polarize such that it isaligned with the electronic field. Maximum polarization is achievedwhere the bridge is coplanar with the other pi systems (i.e., anglebetween, for example, 0° and 10°, or a range which is slightly lesser orgreater), since such an alignment allows facile electronic communicationbetween each molecular section. This produces a more (e.g., highly)conductive state, relative to the state of effective operation as aninsulator, with a much smaller band gap.

When an external electronic field of opposite polarity is applied to themolecule in its “on” state, electrostatic repulsion between theelectronic field and the polarized molecular dipole forces the moleculeto adopt a different conformation. The segments of themolecule—acceptor, donor, and bridge—turn relative to one another, whichresults in a non-planar alignment. Electronic communication betweenacceptor and donor segments is cut off, which prevents electrondelocalization through the molecular system. Accordingly, the moleculeis stable in this highly localized insulating state (i.e., “off” state)as well as in its highly conducting state (i.e., a bistable switch).

The “on” state of the switch permits an electron to easily tunnel intothe molecular system through a short interface between an electrode andthe electronic donor. The electron can subsequently travel through thedelocalized orbitals of the molecular system and exit from the other endof the electrode to complete its path. In contrast, the tunnelingcurrent in an “off” state is essentially zero (i.e., 10⁻⁶ or smaller),and a higher voltage (e.g., 2.5 eV or more) can be used to inject anelectron or hole into either the electronic donor or acceptor.

An aromatic ring system is a compound that has the ability to sustain aninduced ring current. See Smith, M. B.; March, J. March's AdvancedOrganic Chemistry, 5^(th) ed.; John Wiley & Sons, Inc.: New York, 2001;pp. 46-71, the disclosure of which is hereby incorporated by referencein its entirety. Examples of aromatic systems include, withoutlimitation, the following: six-membered rings such as benzene andpyridine; five-membered ring systems such as pyrrole, thiophene andfuran; polyaromatic compounds such as naphthalene, anthracene andpyrene; and, linked aromatic rings such as biphenyl.

Aromatic ring systems can be either substituted or unsubstituted. Asubstituted aromatic ring system possesses a chemical group covalentlyattached to it. Examples of chemical groups include, without limitation,linear alkyl, branched alkyl, cyclic alkyl, aromatic ring systems,substituted aromatic ring systems, electron donating groups, andelectron withdrawing groups. Linear alkyl groups may be relatively small(e.g., C₁ to C₆), of medium length (e.g., C₇ to C₁₂), or larger (e.g.,C₁₃ and above). Branched alkyl groups include, for example, isopropyl,isobutyl, and sec-butyl; and, cyclic alkyl groups include cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl and theirsubstituted derivatives.

An electron donating group is group that can provide electron density toan aromatic ring system through electron delocalization, typicallythrough a π-system. Examples of electron donating groups include,without limitation, —O—, —OH, —OR₁, —NH—, —NH₂, —NHR₁, —NR₁R₂, —PHR₁,—PR₁R₂, —S—, —SH, —SR₁, F, Cl, Br, and I. R₁ and R₂ are substituentsindependently selected from linear alkyl (e.g., methyl), branched alkyl,cyclic alkyl, and an aromatic ring system. The alkyl groups and aromaticring systems may further be substituted with a variety of substituents(e.g, “clipping” substituents such as —SH, which binds to gold or silversubstrates).

An electron withdrawing group is a group that can take electron densityaway from an aromatic system through electron delocalization, typicallythrough a pi system. Examples of electron withdrawing groups include,without limitation, —C(═O)H, —C(═O)R₃, —C(═O)OR₃, —C(═O)OH, —CN, —N═O,—NO₂, —N═N—, CH═NR₃, —CR₃═NR₄, —C═C(CN)₂, —C═C(COR₃)₂, —C═C(CO₂R₃)₂,—C═C(COR₃)CO₂R₄, —SO₂OH, —SO₂OR₃, —S(═O)—R₃, —SO₂R₃, —BH₂, —BHR₃,—BR₃R₄, —PO₃H₂, —PO₃R₃R₄. R₃ and R₄ are substituents independentlyselected from linear alkyl (e.g., methyl), branched alkyl, cyclic alkyl,and an aromatic ring system. The alkyl groups and aromatic ring systemsmay further be substituted with a variety of substituents (e.g.,“clipping” substituents such as —SH, which binds to gold or silversubstrates).

The switchable bridge can be a pi system that can be switched on or offusing an external electric field. The bridging group is either directlyor indirectly connected to the electronic donor, electronic acceptor orboth. It typically is an aromatic ring (e.g., phenyl), a single atom(e.g., —S—, —N—, —O—, —P—), or an atomic group (e.g., —C═C—, —CH₂C(O)—,—NHC(O)). When the group is an atomic group, it is switchable between an“on” state (i.e., conjugated state) and an “off” state (i.e.,non-conjugated state) through tautomerization (e.g., —CH₂C(O)— to—CH═C(OH)— and —NH—C(O)— to —NH═C(OH)—). Examples of switchable bridgesinclude, without limitation, —CH═CH—, —CH═CR₅—, —CR₅═CR₆—, —CH₂C(═O)— or—CH═C(OH)—, —CR₅HC(═O)— or —CR₅═C(OH)—, —CC—, —N═N—, —N═CH—, —NH—CO— or—N═C(OH)—, —N═C(NH₂)—, —N═C(SH)—, —NCS—, —NH—O— and —NHNH—. R₅ and R₆are substituents independently selected from linear alkyl (e.g.,methyl), branched alkyl, cyclic alkyl, and an aromatic ring system.

FIG. 1 shows an exemplary subclass of molecules (10) disclosed herein.The acceptor unit is designated as 11; the switchable bridge isdesignated as 12; and, the donor unit is designated as 13. “EWG” is theelectron withdrawing group (e.g., —NO₂ or —CN), and “EDG” is theelectron donating group (e.g., —NR₁R₂ where R₁ and R₂ are linear alkylgroups substituted with a “clipping” substituent). The units “G₁-G₂” and“G₃-G₄” are bridging groups as described in the preceding paragraph.Optional “adhering units” are shown as X₁ and X₂. The units provide forweak bi-stability (e.g., hydrogen bonding) between adjacent benzenerings and are independently selected from the following chemical groups:hydrogen; a heteroatom such as F, Cl, Br, and I; heteroatom containingfunctional groups such as —OH, —SH, or —NH₂; and substitutedhydrocarbons. Variable position “Z” is an optional tuning atom, oratomic group, that can be used to tune the molecule's electronicproperties. It is selected from a group of atomic units consisting of—CH═, —N═, —S—, —O—, and —P═.

FIG. 2 shows another exemplary subclass of molecules (20). The acceptorunit is designated 21 and possesses an —NO₂ electron withdrawing group;the switchable bridge is designated 22 and includes the tautomerized(i.e., enol) form of a ketone; and the donor unit is designated 23 andcontains an —NHR₁ group as an electron donating group. As with compound11 described above, X is a “adhering unit.”

Molecules disclosed herein can be synthesized using any suitable method.Organotransition metal cross-coupling reactions, however, areparticularly useful for the production of the instant compounds.

FIG. 3 shows a synthetic scheme (30) for the production of compound 20(FIG. 2), where X is hydrogen. Compound 31,7′-bromo-9,9,9′,9′-tetramethyl-9H,9′H-[2,2′]bifluoreny-7-ylamine, isacetylated and subsequently coupled with trimethylsilylacetylene toprovideN-(9,9,9′,9′-tetramethyl-7′-trimethylsilanylethynyl-9H,9′H-[2,2′]bifluorenyl-7-yl)-acetamide32. Trimethylsilyl derivative 32 is subjected to an organometalliccross-coupling reaction in the presence of 4-iodo-nitrobenzene to affordN-[9,9,9′,9′-tetramethyl-7′-(4-nitro-phenylethynyl)-9H,9′H-[2,2′]bifluoreny-7-yl]-acetamide33. Acetylene 33 is converted to ketone34—2-(7′-amino-9,9,9′,9′-tetramethyl)-9H,9′H-[[2,2′]bifluoreny-7-yl]-1-(4-nitro-phenyl)-ethanone—throughthe addition of H₂O, which also effects the hydrolysis of the terminalacetamide. Alkylation of 34 provides the desired compound 35,2-[7′-(2-mercapto-ethylamino)-9,9,9′,9′-tetramethyl-9H,9′H-[2,2′]bifluoreny-7-yl]-1-(4-nitro-phenyl)-ethanone.

Molecular switches containing compounds of the above-recited moleculeclasses are also described herein. FIG. 4 illustrates an exemplaryswitch (40) using a generic compound (43) disclosed herein. Compound 43is placed between two terminals, 41 and 42, through which an electricfield can be applied. The electronic acceptor “A” is proximal orconnected to terminal 41, while the electronic donor “D” is proximal orconnected to terminal 42.

The exemplary switch is further illustrated in FIG. 5, which shows theinclusion of molecule subclass 10 into the switch (50). Compound 10 isplaced between two terminals, 51 and 52. The electronic acceptor 53(i.e., EWG) is proximal to terminal 51. The electronic donor 54 (i.e.,EDG) is attached to terminal 52 through “clipping” substituent 55. Aclipping substituent refers to di-substituted mercaptoalkyl groups. Itcan be a di-substituted-2-mercaptoethyl group in the FIG. 5 example.Likewise, compound 20 can be placed between two electrodes.

Methods of electronic switching can use compounds of the above-recitedmolecule classes. FIG. 6 illustrates such a method (60) using a genericcompound disclosed herein (61). Compound 61 is placed between twoterminals, 62 and 63. Element 64 is the electronic acceptor portion of61; 65 is the bridge portion; and, 66 is the electronic donor portion.As shown in 67, the switch is in an “off” state (i.e., nonconducting):bridge 65 is out of plane, which inhibits electronic communicationbetween 64 and 65. This is due to the presence of an electric fieldwhere terminal 62 is negatively charged and terminal 63 is positivelycharged. Conformation 68 is a transition state where each of compound61's units are coplanar. In conformation 69, an electric field ofopposite polarity to that of 67 is applied, producing an “on” state(i.e., conducting). Electronic communication among the three coplanarunits of 61 results in polarization of the compound: acceptor portion 64bears at least a partial negative charge while donor portion 66 bears atleast a partial positive charge.

A method of switching is further illustrated in reference to FIGS. 7 and8. FIG. 7 illustrates the method using molecule class 10. Compound 10 isplaced between two terminals, 71 and 72. Section 73 is the electronacceptor portion of 10, while sections 74 and 75 are the bridge andelectron donor portions respectively. Conformation 76 represents the“off” stage for the switch; bridge portion 74 is out of plane, whichinhibits electronic communication between 73 and 75. Conformation 77 isa transition state for the switch, where the bridging portion 74 istraveling toward planarity. Upon reaching substantial planarity,conformation 78 is produced and the switch is “on.” This conformationallows molecular portions 73 and 74 to electronically communicate.Compound 10 polarizes, producing at least a partial negative charge onthe electron withdrawing group (i.e., EWG) and at least a partialpositive charge on the electron donating group (i.e., EDG).

FIG. 8 illustrates an exemplary method (80) where the compound of themolecular switch includes a switchable bridge. Compound 20 is placedbetween two terminals, 81 and 82. As shown in conformation 86—an “off”state where there is complete molecular depolarization—portion 83,bridge 84, and donor portion 85 are not coplanar; bridge 84 furthercontains a ketone moiety. Compound 20 comes to substantial coplanarityin conformation 87, but electronic communication throughout the moleculeis inhibited since the ketone moiety interrupts the communicationpathway (i.e., π-system). Providing an electric field of oppositepolarity, as in conformation 88, induces tautomerization of the ketoneto produce an enol. The produced, continuous pi system in the presenceof the electric field effects complete compound polarization (89).

The molecular switches disclosed herein can be used to produceelectronic devices that possess functional length scales measured innanometers. This ability is the direct result of the molecules, switchesand methods described above.

It will be appreciated by those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. The presently disclosedembodiments are therefore considered in all respects to be illustrativeand not restricted. The scope of the invention is indicated by theappended claims rather than the foregoing description and all changesthat come within the meaning and range and equivalence thereof areintended to be embraced therein.

1. A molecular diode switch comprising: a compound having the followingstructure:

wherein: “EWG” is selected from the group consisting of —C(═O)H,—C(═O)R₃, —C(═O)OR₃, —C(═O)OH, —CN, —N═O, —NO₂, —N═N—, CH═NR₃, —CR₃═NR₄,—C═C(CN)₂, —C═C(COR₃)₂, —C═C(CO₂R₃)₂, —C═C(COR₃)CO₂R₄, —SO₂OH, —SO₂OR₃,—S(═O)—R₃, —SO₂R₃, —BH₂, —BHR₃, —BR₃R₄, —PO₃H₂, and —PO₃R₃R₄, wherein R₃and R₄ are substituents independently selected from linear alkyl,branched alkyl, cyclic alkyl, and an aromatic ring system, and whereinthe alkyl substituents are substituted or unsubstituted, “EDG” isselected from a group consisting of —O⁻, —OH, —OR₁, —NH⁻, —NH₂, —NHR₁,—NR₁R₂, —PHR₁, —PR₁R₂, —S⁻, —SH, —SR₁, F, Cl, Br, and I, wherein R₁ andR₂ are substituents independently selected from linear alkyl, branchedalkyl, cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted, X₁ and X₂ areindependently selected from a group consisting of hydrogen, —F, —Cl,—Br, —I, —OH, —SH, —NH₂; and substituted alkyl groups, G₁-G₂ and G₃-G₄are independently selected from a group consisting of —CH═CH—, —CH═CR₅—,—CR₅═CR₆—, —CH₂C(═O)—, —CR₅HC(═O)—, —CC—, —N═N—, —N═CH—, —NH—CO—,—N═C(NH₂)—, —N═C(SH)—, —NCS—, —NH—O— and —NHNH—, wherein R₅ and R₆ aresubstituents independently selected from linear alkyl, branched alkyl,cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted, and Z is selected from agroup of atomic units consisting of —CH═, —N═, —S—, —O—, and —P═; andtwo electrodes in operable contact with the compound such that EWG isproximal or connected to one electrode and EDG is proximal or connectedto another electrode.
 2. A molecular diode switch comprising: a compoundhaving the following structure:

wherein: “EWG” is selected from a group consisting of —C(═O)H, —C(═O)R₃,—C(═O)OR₃, —C(═O)OH, —CN, —N═O, —NO₂, —N═N—, CH═NR₃, —CR₃═NR₄,—C═C(CN)₂, —C═C(COR₃)₂, —C═C(CO₂R₃)₂, —C═C(COR₃)CO₂R₄, —SO₂OH, —SO₂OR₃,—S(═O)—R₃, —SO₂R₃, —BH₂, —BHR₃, —BR₃R₄, —PO₃H₂, —PO₃R₃R₄, wherein R₃ andR₄ are substituents independently selected from linear alkyl, branchedalkyl, cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted, “EDG” is selected from agroup consisting of —O—, —OH, —OR₁, —NH⁻, —NH₂, —NHR₁, —NR₁R₂, —PHR₁,—PR₁R₂, —S⁻, —SH, —SR₁, F, Cl, Br, and I, wherein R₁ and R₂ aresubstituents independently selected from linear alkyl, branched alkyl,cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted, X is selected from agroup consisting of hydrogen, F, Cl, Br, I, —OH, —SH, —NH₂; andsubstituted alkyl groups, and G₁-G₂ is selected from a group consistingof —CH═CH—, —CH═CR₅—, —CR₅═CR₆—, —CH₂C(═O)—, —CR₅HC(═O)—, —CC—, —N═N—,—N═CH—, —NH—CO—, —N═C(NH₂)—, —N═C(SH)—, —NCS—, —NH—O— and —NHNH—,wherein R₅ and R₆ are substituents independently selected from linearalkyl, branched alkyl, cyclic alkyl, and an aromatic ring system, andwherein the alkyl substituents are substituted or unsubstituted; and twoelectrodes in operable contact with the compound such that EWG isproximal or connected to one electrode and EDG is proximal or connectedto another electrode.
 3. A method of electronic switching, comprising:applying an electric field of a first polarity to a compound having a pisystem to cause a first conformational change in the compound thatallows electron conductance through the compound's pi system, thecompound having the structure:

wherein: “EWG” is selected from a group consisting of —C(═O)H, —C(═O)R₃,—C(═O)OR₃, —C(═O)OH, —CN, —N═O, —NO₂, —N═N—, CH═NR₃, —CR₃═NR₄,—C═C(CN)₂, —C═C(COR₃)₂, —C═C(CO₂R₃)₂, —C═C(COR₃)CO₂R₄, —SO₂OH, —SO₂OR₃,—S(═O)—R₃, —SO₂R₃, —BH₂, —BHR₃, —BR₃R₄, —PO₃H₂, and —PO₃R₃R₄, wherein R₃and R₄ are substituents independently selected from linear alkyl,branched alkyl, cyclic alkyl, and an aromatic ring system, and whereinthe alkyl substituents are substituted or unsubstituted, “EDG” isselected from a group consisting of —O⁻, —OH, —OR₁, —NH⁻, —NH₂, —NHR₁,—NR₁R₂, —PHR₁, —PR₁R₂, —S⁻, —SH, —SR₁, F, Cl, Br, and I, wherein R₁ andR₂ are substituents independently selected from linear alkyl, branchedalkyl, cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted, X₁ and X₂ areindependently selected from a group consisting of hydrogen, —F, —Cl,—Br, —I, —OH, —SH, —NH₂; and substituted alkyl groups, G₁-G₂ and G₃-G₄are independently selected from a group consisting of —CH═CH—, —CH═CR₅—,—CR₅═CR₆—, —CH₂C(═O)—, —CR₅HC(═0)—, —CC—, —N═N—, —N═CH—, —NH—CO—,—N═C(NH₂)—, —N═C(SH)—, —NCS—, —NH—O— and —NHNH—, wherein R₅ and R₆ aresubstituents independently selected from linear alkyl, branched alkyl,cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted, and Z is selected from agroup of atomic units consisting of —CH═, —N═, —S—, —O—, and —P; andapplying an electric field of a second, opposite polarity to thecompound to cause a second conformational change in the compound thatinhibits electron conductance through the compound's pi system, whereinthe electric field is provided by two electrodes in operable contactwith the compound such that EWG is proximal or connected to oneelectrode and EDG is proximal or connected to another electrode.
 4. Amethod of electronic switching, comprising: applying an electric fieldof a first polarity to a compound having a pi system to cause a firstconformational change in the compound that allows electron conductancethrough the compound's pi system, the compound having the structure:

wherein: “EWG” is selected from a group consisting of —C(═O)H, —C(═O)R₃,—C(═O)OR₃, —C(═O)OH, —CN, —N═O, —NO₂, —N═N—, CH═NR₃, —CR₃═NR₄,—C═C(CN)₂, —C═C(COR₃)₂, —C═C(CO₂R₃)₂, —C═C(COR₃)CO₂R₄, —SO₂OH, —SO₂OR₃,—S(═O)—R₃, —SO₂R₃, —BH₂, —BHR₃, —BR₃R₄, —PO₃H₂, —PO₃R₃R₄, wherein R₃ andR₄ are substituents independently selected from linear alkyl, branchedalkyl, cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted, “EDG” is selected from agroup consisting of —O⁻, —OH, —OR₁, —NH⁻, —NH₂, —NHR₁, —NR₁R₂, —PHR₁,—PR₁R₂, —S⁻, —SH, —SR₁, F, Cl, Br, and I, wherein R₁ and R₂ aresubstituents independently selected from linear alkyl, branched alkyl,cyclic alkyl, and an aromatic ring system, and wherein the alkylsubstituents are substituted or unsubstituted, X is selected from agroup consisting of hydrogen, F, Cl, Br, I, —OH, —SH, —NH₂; andsubstituted alkyl groups, and G₁-G₂ is selected from a group consistingof —CH═CH—, —CH═CR₅—, —CR₅═CR₆—, —CH₂C(═O)—, —CR₅HC(═O)—, —CC—, —N═N—,—N═CH—, —NH—CO—, —N═C(NH₂)—, —N═C(SH)—, —NCS—, —NH—O— and —NHNH—,wherein R₅ and R₆ are substituents independently selected from linearalkyl, branched alkyl, cyclic alkyl, and an aromatic ring system, andwherein the alkyl substituents are substituted or unsubstituted; andapplying an electric field of a second, opposite polarity to thecompound to cause a second conformational change in the compound thatinhibits electron conductance through the compound's pi system, whereinthe electric field is provided by two electrodes in operable contactwith the compound such that EWG is proximal or connected to oneelectrode and EDG is proximal or connected to another electrode.